(a) Field of the Invention
The present invention pertains to planar type electroacoustic transducers which are employed in headphones, loadspeakers, microphones or like devices.
(b) Description of the Prior Art
As electroacoustic transducers for converting electric signals to acoustic signals or for converting acoustic signals to electric signals, there have been developed various types of transducers including electrostatic type and electrodynamic type transducers. As electroacoustic transducers for use in, for example, headphones, there have been developed transducers of electrodynamic and planar types. As such example, FIG. 1 shows a diagrammatic partial plan view of a known planar type electroacoustic transducer arrangement. FIG. 2 is a sectional view taken along II--II in FIG. 1. In FIG. 1, there is provided, on a planar type diaphragm 1, a flexible electric conductor 2 in a wave-like pattern. A magnet plate 3 is arranged beneath the diaphragm 1 as shown in FIG. 2. This conductor 2 has straightly extending portions and curved portions which connect adjacent straightly extending portions to each other. The magnet plate 3 is provided with parallel rows of magnetic poles which are arranged to change in alternate fashion from one row to another. The straightly extending portions of the electric conductor 2 are arranged to be positioned between the respective rows of the magnetic poles so that each row having the same single pole extends along the straightly extending portions of the electric conductor 2. The magnetic fields which are produced at the straightly extending portions of the electric conductor 2 by these magnetic poles are indicated at symbols A, A, . . . in FIG. 2. Broken lines in FIG. 2 represent a part of the lines of magnetic flux.
The operation of the electroacoustic transducer shown in FIGS. 1 and 2 is as follows. If an electric current is caused to flow through the electric conductor 2 in the direction indicated by the arrow B shown in FIG. 1, a force acts on every portion of the conductor 2, excluding the curved portions thereof, in the direction indicated by the arrow E shown in FIG. 2 in accordance with Fleming's left-hand rule, so that the diaphragm 1 is lifted upwardly in FIG. 2. Conversely, if an electric current is caused to flow through the electric conductor 2 in a direction opposite to that shown by the arrow B in FIG. 1, the diaphram 1 is caused to descend downwardly in FIG. 2 toward the magnet plate 3. Thus, if a current carrying audio signal is caused to flow through the conductor 2, the diaphragm 1 will vibrate upwardly and downwardly in FIG. 2 in accordance with the current of the audio signals, so that the electric signals can be converted to acoustic signals.
However, in such known electroacoustic transducer as mentioned above, especially in conventional planar types of such devices, the electric conductor provided on a diaphragm is oriented to run merely in upgoing and downgoing directions on the diaphragm, and thus, there is the disadvantage that partial vibrations of the diaphragm tend to appear at sites between the adjacent runs of the conductor. Moreover, in such a conventional electroacoustic transducer, the diaphragm is simply flat in shape, and accordingly the diaphragm is poor in rigidity, and this also causes nodes of vibration mode to develop at portions of the diaphragm located between adjacent runs of the conductor, leading to development of partial vibrations.